1. Field of the Invention
This invention relates to a chemically amplified positive resist composition which is highly sensitive to actinic radiation such as deep-UV, electron beam and X-ray, can be developed with alkaline aqueous solution to form a pattern, and is thus suitable for use in a fine patterning technique.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. The current patterning technology mostly relies on light exposure which is now approaching the essential limit of resolution which is dictated by the wavelength of a light source. It is generally recognized that in light exposure using g-line (wavelength 436 nm) or i-line (wavelength 365 nm) as a light source, a pattern rule of about 0.5 .mu.m is the limit. For LSIs fabricated by such light exposure technique, a degree of integration equivalent to 16 mega-bit DRAM is the limit. At present, LSIs fabricated in the laboratory have reached this stage. It is urgently required to develop a finer patterning technique.
Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.3 .mu.m or 0.4 .mu.m. If a less light absorbing resist is used, it is possible to form a pattern having a side wall nearly perpendicular to the substrate. Advanced engineers place focus on the utilization of high illuminance KrF excimer laser as a deep-UV source. A resist material having high resolution and sensitivity must be developed before such an excimer laser can be used in a mass scale manufacturing technique.
In this respect, recently developed chemical amplification positive resist materials using acid catalysts as disclosed in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. No. 4,491,628 and 5,310,619 are regarded promising as resist materials especially suited for deep-UV lithography because these materials have relatively high sensitivity, resolution and dry etching resistance. The chemically amplified, positive resist materials being known include those of the two-component system comprising an alkali-soluble base resin and a photoacid generator and those of the three-component system comprising an alkali-soluble base resin, a photoacid generator, and a dissolution inhibitor having an acid labile group. It is desired to further improve the resolution and heat resistance during dry etching of such resist materials.
Use of an acid labile group different from common acid labile groups such as tert-butoxycarbonyl and tert-butyl groups as used in the aforementioned chemical amplification positive resist compositions is proposed in JP-A 83055/1994 and 128859/1995 which disclose chemical amplification positive resist compositions using an acid labile group of acetal type. It is also desired to further improve the resolution and heat resistance during dry etching of these resist materials.
JP-A 230574/1994 discloses a chemically amplified positive resist composition comprising a linear polymer having an acid group (e.g., carboxylic acid, sulfonic acid and phenolic hydroxyl group), a photoacid generator, and a compound having at least two vinyl ether groups in a molecule. In this resist composition, the compound having at least two vinyl ether groups in a molecule is contained for the purpose of alkali dissolution control. Since the base resin has increased alkali dissolution, the vinyl ether group-containing compound must be contained in a large amount, with possible generation of scum upon development. If the amount of the vinyl ether group-containing compound added is reduced, there occurs shortage of dissolution contrast and hence, a decline of resolution. It is thus desired to further improve resolution and suppress scum generation.
Furthermore, JP-A 265213/1993 discloses a chemically amplified positive resist composition comprising a polymer containing a phenolic hydroxyl group replaced by a 2-vinyloxyalkylene group and a photoacid generator. Since the 2-vinyloxyalkylene group is not an acid labile group, the polymer is less alkali soluble. Low dissolution contrast results in shortage of resolution. It is thus desired to further improve resolution.